Capacitive touch technology has become relevant in an increasing number of applications, particularly in mobile hand-helds, netbooks and laptop computers. Compared to other touch technologies, capacitive touch enables very sensitive response as well as other features, such as multi-touch. Optically clear adhesives (OCAs) are often used for bonding purposes (e.g., attachment of different conductive layers) in the capacitive touch panel assembly. Not only do OCAs provide a mechanical bonding function, but they can also greatly increase the optical quality of the display by eliminating air gaps that reduce brightness and contrast.
There is currently an increasing need for soft OCAs. A “soft” OCA is defined as having low modulus and high tan delta values from dynamic mechanical analysis (DMA). These soft OCAs are desirable to enable better wetting of thick inks (e.g., 50 μm) on the display. Additionally, as a result of the display module assembly process, they can improve stress relief. Such stress relieving features are beneficial to reduce potential defects, such as Mura, when bonding a liquid crystal module and to minimize delayed-bubble formation.
However, because soft OCAs have to be both soft enough to conform and yet strong enough to bond, they can suffer from process disadvantages. It can be difficult to balance the need to be soft enough to conform and yet strong enough to bond in one material. Liquid OCAs (LOCAs) can be advantageous because they are flowable and can later be cured to build in internal strength to provide a bond. However, LOCAs also have certain process disadvantages as well. For example, while they can easily flow into the desired areas, they can also easily flow into undesired areas. In addition, the curing step means there is room for final assembly error if the cure is not sufficient. The curing step also adds time to the total assembly process.